GIS and side scan sonar were used to assess spatial and temporal expansion of exotic mussels, Dreissena sp., onto sedimentary habitats in Lake Erie. Data on substrate type, bathymetry, distance from shore, and change through time in years were incorporated into a GIS database that was used to model percent cover of Dreissena. Substrate and change over time contributed significantly to the model. Built with 1994 - 1997 data, the model explained 55.9% of the variability in Dreissena coverage, and was tested with data from 1998. Errors between original sonar data and mussel coverage predicted from the model were <20%. Estimates of percent coverage of Dreissena were lowest for fine-grained and highest for coarse-grained sediments. Dreissena populations across all substrates in Lake Erie have been increasing since 1994 at an estimated average rate of 1000.5 km2/yr ± 6.3 km2/yr, and presently occupy 5484.1 km2 ± 31.74 km2 of the 25,734.1 km2 of Lake Erie. This model presents strong evidence of expanding Dreissena populations in Lake Erie during the past 4 years, demonstrating that watersheds invaded by Dreissena are extremely dynamic benthic habitats.